REPRODUCTION 517 



The female gamete is more uniform, being generally a larger 

 mass of protoplasm, with no cell- wall, and in all but the low^est 

 forms incapable of motion. Below the Chlorophycese it is 

 always set free and is fertilised in the water ; in and above that 

 group it remains in the cell in which it is produced, an oogonium 

 or an archegonium as the case may be. In the Angiosperms it 

 is not even developed in an archegonium. A curious peculiarity- 

 is noticeable in the Rhodophyceae, where the female organ, 

 known as a procarp, contains no differentiated female cell. In 

 the Ascomj'cetous fungi the same absence of differentiation is 

 seen, though possibly here there is no sexuality. 



The peculiarity of sexual reproduction is that the gametes 

 are incapable of giving rise to a new individual without fusion 

 of a male and female together. In this process nucleus unites 

 with nucleus and protoplasm with protoplasm. In the fusion of 

 the nuclei in the Phanerogams, however, the chromosomes do 

 not unite, so that the nucleus of the zygote or fertilised cell has 

 twice the number of these that that of each gamete possessed. 

 When the zygote germinates, the first nuclear division is so 

 carried out that each daughter- nucleus receives half the chromo- 

 somes from each sexual nucleus. 



The cells which fuse may be alike, or may be dissimilar ; in 

 the former case the process is spoken of as conjugation, in the 

 latter case fertilisation. The resulting body is called the 

 zygospore or the oospore respectively ; the term ' zygote ' is 

 now generally used instead of either of these. Conjugation only 

 occurs among the comparatively undifferentiated Thallophyta. 



The mode of bringing the gametes together varies with the 

 habit of life of the plants. "Where the antherozoid is motile it 

 makes its way .to the oosphere by means of its cilia, which 

 enable it to swim freely in water. In those forms with a 

 terrestrial habit, such as the Bryophyta and Pteridophyta, in 

 which the antherozoid is ciliated, fertilisation can only be 

 brought about when the gametophytes are moistened, as is 

 the case from time to time. The antherozoids are attracted to 

 the archegonia b}' some constituent of the mucilaginous matter 

 which is excreted from their necks when they open. In the 

 Mosses this has been ascertained to be cane-sugar; in the Ferns 

 it is malic acid or one of its salts. In the Rhodophyceae and 

 such Ascomycetes as possess sexual reproduction the passive 

 male gamete, known as a spermatium, is floated to the female 

 organ or its trichogyne by currents in the water. 



In the Phanerogams, where the female gametophyte is always 



